Photovoltaic (PV) systems generally include numerous PV strings, where each PV string can include a number of PV modules that are connected in series and/or in parallel. Each PV module, in turn, includes an array of solar cells, and each solar cell collects solar radiation for conversion into usable current.
Roof-mounted PV systems complying with the 2011 National Electrical Code® (NEC) and all PV systems complying with the 2014 NEC include an arc-fault detector (AFD) to determine the presence of an arc-fault. Detecting and de-energizing of arc-faults are critical to minimize uncontrolled electrical fires. Many AFDs use frequency content of the PV string for arc detection. For instance, arc-faults are associated with high frequency noise in the PV string. However, noise can also arise from other sources in the PV system, such as electromagnetic coupling (crosstalk), inverter switching, and other radio frequency (RF) effects. To minimize false identification of arc-faults, AFDs generally measure current or voltage over multiple frequencies. The presence of a spike in AC noise across multiple frequencies provides a greater likelihood that an arc-fault is present in the PV system.
Although AFDs can detect the presence of an arc-fault, they cannot provide the location of such an arc-fault. Thus, the topology of some PV systems employs multiple AFDs, where at least one AFD is associated with each PV string. In this way, if the AFD for that particular PV string detects an arc-fault, then that AFD provides a signal to a switch in order to isolate and de-energize that PV string. Such a topology can be very costly and inefficient, especially if a system has numerous PV strings, thereby necessitating numerous AFDs. Thus, additional systems and methods are required for selectively identifying the location of an arc-fault and isolating the PV strings associated with that arc-fault location.